The present invention relates to an apparatus and a method for measuring ammonia in liquid and controlling the treatment thereof, more particularly, to apparatus for real time measuring the amount of ammonia in liquid with or without suspended solids in a biochemical process and using the results of such measuring to control selected aspects of the process.
The prior art has employed many devices and systems to process and purify water from industrial operations and municipal sources prior to discharging the water. Wastewater treatment plants (WWTP""s ), which are well known in the art, have been most often utilized to address this problem. Additionally, many industrial and municipal water treatment plants utilize biological systems to pre-treat their wastes prior to discharging into the usual municipal treatment plant.
Microorganisms used in the sludge break down or degrade contaminants for the desired water treatment in these processes. Efficient process performance and control requires quick and accurate assessment of information on the activity of the microorganisms. This has proven to be a difficult task in view of the wide variety of materials and contaminants that typically enter into treatment systems. Also, variations in the quantity of wastewater being treated, such as daily, weekly or seasonal changes, can dramatically change numerous important factors in the treatment process, such as pH, temperature, dissolved oxygen, nutrients and the like, alteration of which can be highly detrimental to proper wastewater treatment. Improperly treated wastewater poses serious human health dangers.
Various biological nutrient removal (BNR) processes are often used in biochemical systems/plants/processes. xe2x80x9cBNRxe2x80x9d is used hereinafter in a very generic sense, namely any biochemical process that uses microorganisms to remove nutrients. In BNR processes, contaminants in liquids such as wastewater, particularly carbon sources (measured as biochemical oxygen demand or BOD), ammonia, nitrates, phosphates and the like are digested by activated sludge in anaerobic, anoxic and aerobic (oxic) stages, also known in the art. In the anaerobic stage, wastewater, with or without passing through a preliminary settlement process, is mixed with return activated sludge (RAS), sometimes hereinafter referred to as xe2x80x9cmixed liquor.xe2x80x9d
It is, of course, important to quantify the various contaminants in the wastewater. One of those contaminants that is important to quantify is the amount of ammonia. This is because quantification of the amount of ammonia provides valuable information about nitrification/dentrification processes, for example. Various system parameters such as retention time can be altered to enhance the process and increase treatment system efficiency in response to this important information.
A wide variety of methods have been attempted to measure the amount of ammonia in wastewater. However, there have been a number of serious drawbacks in obtaining accurate ammonia quantities on a real time basis. One significant drawback has been the need to filter wastewater samples prior to measuring the amount of ammonia. This is a severe constraint on the real time ability to obtain accurate ammonia readings. Prior art known to the inventors includes the following U.S. Pat. Nos.: 3,354,057; 3,565,583; 3,616,273; 3,877,875; 4,162,195; 4,209,299; 4,216,065; 4,277,343; 4,297,173; 4,666,610; 5,466,604 and 5,641,966.
It is an object of the present invention to provide apparatus and a method for measuring the amount of ammonia in biochemical systems to maximize the efficiency of the treatment process.
It is a further object of the present invention to provide apparatus and a method for real-time measuring of the amount of ammonia in liquids to enhance control of the biochemical process, to maximize process performance in response to transient and other conditions.
Other objects of the present invention will be apparent to those of ordinary skill in the art based on the following drawings, detailed description of preferred embodiments and the appended claims.
One aspect of the invention includes apparatus for measuring ammonia in liquids, especially wastewater. It includes a wastewater sample container having a fluid flow opening connected to a fluid supply; optionally, a pH probe positioned to detect the pH of samples in the container and an ammonia probe positioned to detect ammonia in the samples. A pH adjustment supply connects to the container and an ammonia adjustment supply connects to the container. Optionally, a pH analyzer is adapted to determine changes in sample pH and an ammonia analyzer is adapted to determine changes in the quantity of ammonia in the samples. A controller connects to 1) the pH adjustment supply to introduce pH adjustment solution into the container, 2) the ammonia adjustment supply to introduce ammonia adjustment solution into the container to periodically calibrate the ammonia probe, 3) the container to introduce samples into and remove samples from the container at selected time intervals, and 4) the optional pH analyzer and the ammonia analyzer to measure ammonia in the samples.
The invention also includes a method of measuring ammonia in liquids, especially wastewater. This method is different from other ammonia analyzing techniques in that there is no need to prepare the sample by filtration or other method of solids removal. The presence of organic solids in the liquid, at an elevated pH, can cause a release of ammonia to the liquid as proteinaceous compounds are hydrolyzed. This ammonia release phenomenon affects the accuracy of the ammonia measurement if not properly addressed. The invention uses a method to determine the rate of ammonia released during the ammonia measurement and compensates for it in its measurement. The method includes isolating a wastewater sample; adjusting the pH of the sample to a predetermined level for a predetermined time interval t1; recording a value of ammonia present in the sample with an ammonia selective probe: recording another value of ammonia present in the sample after another predetermined time interval t2; determining ammonia concentrations in the sample at each predetermined time interval t1 and t2 according to the following formula:
[NH3]=10axc2x7mV+b
wherein a and b are linear coefficients of the ammonia probe; determining the amount of released ammonia from the sample according to the following formula:                     Δ        ⁢                  xe2x80x83                [                  NH          3                ]                    Δ        ⁢                  xe2x80x83                ⁢        t              =                                        [                          NH              3                        ]                    2                -                              [                          NH              3                        ]                    1                                      t          2                -                  t          1                      ;  and
determining the ammonia concentration of the sample according to the following formula:       [          NH      3        ]    =                    [                  NH          3                ]            1        -                            Δ          ⁢                      xe2x80x83                    [                      NH            3                    ]                          Δ          ⁢                      xe2x80x83                    ⁢          t                    ·                        t          1                .            